Donkey-hide gelatin (E-jiao) is an effective medicine for replenishing blood and nourishing Qi. In as early as the Eastern Han Dynasty, it had listed as “top grade medicine” in the famous medicine book “Shen Nong's Herbal Classic”, and it was documented that “taking permanently, it can replenish Qi and cause a feeling of body weight reduction”. The characteristic of Donkey-hide gelatin is Gan, mild-natured, its main function is to replenish blood and nourish Yin, to moisturize dryness, and stop bleeding. It is used for treating blood deficiency chlorosis, dizziness, palpitation, muscle atrophy and weakness, irritability, insomnia, internal agitation of deficient Wind, cough owing to dryness in the lung and over-strain, chatter of blood, vomiting blood and hematuria, stool bleeding, threatened abortion and so on. According to the 2010 edition of Chinese Pharmacopoeia, Donkey-hide gelatin is a solid gelatin produced by boiling the dried or fresh skin of equidae donkey and then concentrating the decoction. However, the molecular weights of collagen proteins are too large (from tens of thousands to hundreds of thousands) to be absorbed by patients with weak spleen and stomach, which result in inadequate performance of functions of Donkey-hide gelatin. Meanwhile, the breeding stocks of donkeys have been declining in recent years, this directly results in inadequate supply of donkey skin, and the rising price of Donkey-hide gelatin. The growing deficiency in the supply of donkey skin material cannot meet the requirements of the market, whereas because of the small-molecule Donkey-hide gelatin by enzymatic hydrolysis on donkey-hide gelatin juice can significantly increase the bioavailability of Donkey-hide gelatin, it can be a good measure to solve the contradiction between supply and demand.
In recent years, researches on enzymolysis of Donkey-hide gelatin have made some progresses, a number of patents have been published, including: (1) “A method for the preparation of liquid Donkey-hide gelatin by enzymolysis”, Publication No. is CN1237421A; (2) “Active Donkey-hide gelatin collagen peptide products”, Publication No. is CN1807653A; (3) “A preparation method for Donkey-hide gelatin hydrolyzate with low molecular weight”, Publication No. is CN101269090A. These three inventions all reported the production of collagen peptides by means of protease digestion of Donkey-hide gelatin. Based on the existing technology, this invention takes advantage of characteristically high proline and hydroxyproline contents in Donkey-hide gelatin, proposes to enzymatically digest it by using proline protease for the first time, results in significantly better hydrolysis than that had been reported in the previous patents. In the above-mentioned 3 patents, most of the molecular weights of the products were distributed in the range of less than 5000 Da, even less than 10000 Da. Besides, none of the patents reported the accurate measurement of molecular weight distribution and the free amino acid contents, whereas in the present invention, the peptide molecular weight is distributed in the range of 200-3000 Da, mainly in 200-1000 Da; in patents CN1237421A and CN1807653A, both of them used the Donkey-hide gelatin lumps with auxiliary material added as the digestion raw material, whereas in the present invention, Donkey-hide gelatin juice is used as the raw material for enzymolysis in order to simplify the process, save cost, and result in products with good solubility and high bioavailability, the clearance rate of DPPH and ABTS radicals are close to 100%.
Many reports in the literature (Adibi A S. America Nutrition, 1984, 25: 1114-1122; DBA Silk Gut, 1974, 15: 494-501) stated that peptides with the molecular weights in the range of 200-1000 Da demonstrated superior absorption and efficacy in comparison with peptides of other size and free amino acids. The present invention proposes to use Donkey-hide gelatin juice without auxiliary material as raw materials, to accurately determine the free amino acid contents in the products and the molecular weight distribution of the products, and the small peptides contained in the products distribute mostly in the range of 200-1000 Da, therefore their absorption and efficacy are better.